Liquid Film Measurements using Electrical Sensors, Infrared Attenuation and Tomography with Neutrons and X-Rays

Electrical film thickness sensors, based on the signal acquisition technique of wire-mesh sensors, are used for a non-intrusive measurement of two-dimensional liquid film thickness distributions in annular flows in fuel rod bundle geometries with a sampling rate of up to 10 kHz. The characteristics of the sensors as function of the electrode geometry and the response to waves is studied by potential field simulations. Miniaturized sensors of this kind, manufactured by photo-lithographic techniques in the clean room extend the range of application to mini-channels.
As an alternative to the electrical sensors, tomography with cold neutrons was applied to identical subchannel geometries, again with and without a spacer grid. The tests were conducted at the spallation neutron source SINQ of PSI. As the main advantage, tomography is contactless and can be applied to non-adiabatic flows in heated subchannels. Derived liquid film thickness distributions have a higher spatial resolution compared to the electrical sensor, while the latter has a superior time resolution. The direct comparison of both techniques has shown a very good agreement of time averaged film thickness profiles. The tomography is currently applied to a heated subchannel using chloroform as working fluid. Heavy water heating was selected instead of electrical heaters to avoid a damage of the test section, the working fluid is chloroform.
A contactless infrared attenuation technique was developed to acquire two-dimensional water film thickness distributions on non-adiabatic walls. It uses an illumination of the observed wall region by near infrared radiation and the recording of the reflected light in a narrow wavelength band. The light is attenuated while passing twice through the water film. The ideal surface is characterized by a diffuse backscattering of the light, which allows an application to many technical wall surfaces. The observation of condensing and re-evaporating liquid films flowing down a vertical wall exposed to a mixture of air and vapor is presented. A second mid-wavelength IR camera is used for a synchronous measurement of the film temperature. Results can be used to validate film flow models for containment analysesShow more